Add blocks from different themes?

Is it possible to add blocks that are in different themes into the site you are building already with a different theme selected?. In the Block section, there's an "add more" option at the very bottom. However, it only showcases the whole list of themes that are available with only the red delete button at the top-right corner. But not an "add button". I believe it was before, not only for purchase, for adding the theme or combining them.

Also, I cannot see the Block Pack for Mobirise 3 (+60 new blocks) that I already have in my account. It just appears the blocks that the theme has. Is kinda of annoying, I suppose to have that.